A.O. Smith VB/VW-500 - Manual (Page 19)

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7. SYSTEM CONTROLLER
Controlling of these systems is decided mainly by the type
of building system controlling desired. A single boiler
installation might be controlled directly from space
temperature thermostat(s). Multiple boiler installations are
more effective when the boilers are sequenced in and out of
operation by some form of main water temperature controller.
With one or two boilers, individual control settings at
progressive temperature may be used. For more than
two boilers, electronic sequencing controlling is
recommended. Individual controls, or the separate stages
of a step controller, should start the boiler loop circulator
and fire the boiler. Some large installations may require the
firing of more than one boiler per stage.
The system or primary circulator may or may not be
controlled by the boiler sequencer. When this pump is
operated through the first switch of any type of step
controller, care should be taken to determine if a motor
starter is needed due to insufficient switch capacity.
Multiple boiler installations are especially adapted to the
use of outdoor reset for main water temperatures. This
feature is not mandatory, but offers smooth, efficient
operation of a modern system.
Normal use of flow control valves is required to prevent
cross circulation of zones as with any multiple pump system.
Large systems with multiple boilers should include main
water temperature controls (with or without outdoor
reset) to sequence the boiler on and off, in relation to
the load on the system.
24VAC System Controller (Optional) - VB models require
a field supplied 24VAC operating control to be installed in
the system such as: loop thermostat, indoor/outdoor reset
control, sequencing panel, or energy management system.
The connection for such devices is located in the junction
box at the rear of the unit. A 24VAC thermostat/aquastat
can only be used as an “On/Off” switch for the unit. The
actual controlling of the phasing will be through either the
inlet or remote probe. To use a 24VAC system controller,
dipswitch “4” on the MCB must be switched to the “on”
position, see REMOTE PROBE INSTALLATION.
INTERNAL CONTAMINANTS
The hydronic system must be internally cleaned and flushed
after a new or replacement boiler has been installed, to remove
contaminants that may have accumulated during installation.
This is extremely important when a replacement boiler is installed
into an existing system where Stop Leak or other boiler
additives have been used.
Failure to clean and flush the system can produce acid
concentrations that become corrosive, and leads to heat
exchanger failure.
All hot water heating systems should be completely flushed
with a grease removing solution to assure trouble-free operation.
Pipe joint compounds, soldering paste, grease on tubing and
pipe all tend to contaminate a system
Failure to flush contaminants from a system can cause solids
to form on the inside of boiler exchangers, create excessive
blockage of water circulation, deterioration of the pumps seal
and impellers.
HOT WATER SUPPLY BOILER SYSTEM-
GENERAL WATER LINE CONNECTIONS
This section provides detailed installation diagrams for a typical
method of application for the unit.
Piping diagrams will serve to provide the installer with a reference
for the materials and methods of piping necessary for installation.
It is essential that all water piping be installed and connected
as shown on the diagrams. Check the diagrams to be used
thoroughly before starting installation to avoid possible errors
and to minimize time and material cost.
It is essential that all water piping be installed and connected
as shown on the diagrams. Check the diagrams to be used
thoroughly before starting installation to avoid possible errors
and to minimize the time and material cost.
HARD WATER CONDITIONS
Where hard water conditions exist, water softening or the
threshold type of water treatment is recommended. This will
protect the dishwashers, coffee urns, water heaters, water piping
and other equipment. When water softening or water treatment
is not practical, a comparatively easy method of periodic lime
removal from the unit may be employed.
SHUTOFF VALVES SHOULD BE INSTALLED FOR SERVICING
BOILER, HOWEVER, LOCAL CODES SHALL GOVERN THEIR
USAGE.
THERMAL EXPANSION (CLOSED SYSTEM)
Thermal expansion occurs in any hot water system when system
water is heated or “recovered” during periods of non-use.
If the system is operated in an “open” condition such as being
connected directly to the city main, the volume of expanded water
generated during the recovery periods can be dissipated back
through the “open” connection to the city main so pressure
cannot build up.
However, once a back flow preventer is installed to isolate system
water from the public supply; or a pressure reducing valve is
installed to protect a water meter; or any device preventing flow
back into the cold water supply, the “open” condition becomes
“closed”. During periods of temperature recovery and no usage,
expanded water has no place to go, so the pressure builds up until
a relief valve opens releasing hot water.
A relief valve opening on pressure will flow small amounts
of water, whereas relieving on temperature releases large
amounts of water.
If your system is closed, some provision must be made for
THERMAL EXPANSION to protect the system from excessive
pressure. Install an expansion tank that is properly and adequately
sized for the expanding volume of water in the system.
Service problems or parts failure due to excessive pressure are
NOT covered under warranty.
REMOTE PROBE INSTALLATION PROCEDURE
A remote probe is supplied with each hot water supply boiler
(VW models). To connect the remote probe to the boiler,
remove the cover from the junction box at the rear of the
unit. Connect the probe wire pigtails, see Figure 7. Check
the field connection diagram located on this cover of the
junction box to assure proper wiring.
Once the remote probe has been connected to the boiler, it
must be designated as the controlling probe for the system.